1. Field of the Invention
The present invention relates to a backlight device, in particular, a backlight device having a light emitting diode as a light source, and a display device using the same.
2. Description of the Related Art
Recently, for example, a liquid crystal display has been used as a flat panel display having features of a thinner body, a lighter weight and the like, as compared to those of a conventional Braun tube, and widely applied for use in a liquid crystal television set, a monitor, a mobile phone and the like. Such a liquid crystal display includes a backlight device for emitting light, and a liquid crystal panel for displaying a desired image by functioning as a shutter for light from a light source that is mounted to the backlight device.
Moreover, for the backlight device, a liquid crystal display of an edge-light type or a direct light type, in which a linear light source constituted of a cold cathode ray tube or a hot cathode ray tube is disposed on a lateral side or a lower side of the liquid crystal panel, is provided. However, the above-described cold cathode ray tube or the like includes mercury, and thus is difficult to be recycled or the like when it is disposed. Then, a backlight device that uses a light emitting diode (LED) with no mercury included as the light source has been suggested (see, for example, JP 2004-21147 A).
Further, the above-described conventional backlight device is provided with light emitting diodes that emit light in three colors of red (R), green (G) and blue (B), respectively, and the colored light in these three colors is mixed so as to obtain white light. Moreover, this conventional backlight device is provided with a sensor for detecting the light from the light emitting diodes, and adjusts light amounts of the respective light emitting diodes of R, G, B based on the detection results, and thereby to change of brightness and color degrees of the corresponding light emitting diodes over the course of time can be suppressed.
By the way, the light amounts of the light emitting diodes as described above are varied significantly. That is, even products of the light emitting diodes with the same design values of various characteristics, such as model numbers, model types, light degrees, rated current values and directivities, may be significantly different in light amount from one another, depending on quality, properties and the like of their semiconductor materials. Moreover, a lighting efficiency of the light emitting diode is easily changed according to a change of environment of use, in particular, a change of its surrounding temperature, compared with a lighting efficiency of a cathode ray tube or the like, and the light amount thereof is also changeable comparatively.
Thus, as described above, the conventional backlight device that is provided with a plurality of the light emitting diodes had a problem in that the light amounts of the plurality of the respective light emitting diodes become non-uniform due to the change of the light emitting efficiencies resulting from the variation of the light amounts of the respective light emitting diodes and the change of the surrounding environment, and unevenness of the brightness of light toward a liquid crystal panel (on the outside) was likely to occur. In particular, when the number of the light emitting diodes to be provided is increased according to an increase of a screen size, brightness or the like of the liquid crystal display, a width of the non-uniformity of the light amounts (a difference between the light amounts of the brightest light emitting diode and the darkest light emitting diode) may be significantly large due to the increase of the number of the light emitting diodes provided, an increase of a heat amount caused thereby and the like. As a result, it became significantly difficult for the conventional backlight device to prevent the occurrence of the brightness unevenness of the light that is directed toward the outside, when increasing the number of the light emitting diodes provided.
Moreover, light emitting diodes with equivalent light amounts are not generally sold, and there may be a new problem in that, in the case of purchasing them while designating their light amounts, brightness and the like, it cannot be avoided that a unit price of the light emitting diode is jumped up and a cost for manufacturing the backlight device is increased.